1. Field of the Invention
This invention relates to a programmable logic controller input/output system.
2. Discussion of the Background
Normally, referring to FIG. 1, a programmable logic controller comprises a processing unit referred to as the CPU and inputs/outputs couplers or interfaces C1, C2, C3, C4 which provide the link between the processing unit CPU and the operations part (sensors, pre-actuators, etc.).
The processing unit CPU comprises processor(s) P, a ROM memory M1 containing the manufacturer's program, a RAM memory M2, an inputs/outputs manager I that communicates with them through a bus. Optionally, couplers such as C4 are integrated in the internal structure of the processing unit. A RAM memory M2 contains the user program in a first area, and data in a second area, particularly images of the states of couplers and constants related to the user program. The user program is written in a specific graphic language such as the LADDER language type (contacts language) or the GRAFCET language type.
Programmable logic controllers to be used to process a large number of inputs-outputs have a modular structure based on one or several "racks" which contain couplers and are connected to each other. The main rack marked R contains the module(s) of processing units CPU.
The inputs-outputs manager I comprises an interface bus IP that provides the link through the inputs-outputs bus with the main rack R couplers C1, C2, or with secondary "rack" R1 couplers connected to the main rack, and also with couplers included in the CPU such as coupler C4. A bus interface IS provides the link with remote couplers such as coupler C3, through a factory bus B.
The programmable logic controller comprising the central processing unit CPU receives electrical signals from sensors through couplers and transmits electrical signals to other couplers. Therefore each coupler controls the operations part under the control of the processing unit CPU. This processing unit continuously executes the user program as a function of the state of its inputs to control the states of the outputs.
Each coupler such as C1, C2, C3, C4 is connected through physical input or output channels 1, 2 etc., to the operations part (sensors, actuators, etc.).
There are several categories of sensors, including simple couplers and intelligent couplers.
Simple couplers transmit information to the processing unit (or receive information from it) without any complementary processing. This is the case for On/Off couplers.
Intelligent couplers carry out processing (filtering, scaling) of signals that they receive or transmit and/or processing of information received from sensors or information sent to the pre-actuator before sending it to the processing unit. For example, the analog value output by a temperature sensor must firstly be digitized and then made linear as a function of calculations taking account of the sensor type. The processing is called job function. Couplers have their own microprocessors and internal software to carry out this processing so that it can be done independently from the processing unit CPU. These intelligent couplers are adapted to one job among communication, analog processing, axis positioning or control, counting, regulation or special treatment (electronic cam, weighing, etc.).
At the present time, coupler operating parameters are controlled by mechanical means (potentiometers, jumpers) or by software means. The user responsible for configuration must change methods when using different couplers.